Method for manufacturing a membrane assembly for a fuel cell with catalyst-free edge to the frame; membrane assembly and fuel cell with membrane assembly

ABSTRACT

A method for manufacturing a membrane assembly for a fuel cell, which membrane assembly includes a membrane with a catalyst layer and a frame arranged on the same side of the membrane and a gap between the catalyst layer and the frame. To allow an easy and cost-effective way for manufacturing such a membrane assembly, the manufacturing method may include the following steps:positioning a first decal layer, which is made of the same material as the first catalyst layer, on the first side of the membrane in a way that the first decal layer overlaps the frame,positioning a second decal layer, which is made of the same material as the second catalyst layer, on the second side of the membrane,pressing the first decal layer and the second decal layer against each other with the membrane and the frame positioned in-between.

The present invention relates to a method for manufacturing a membraneassembly for a fuel cell, which membrane assembly comprises a membranewith a first side and a second side, a first catalyst layer arranged onthe first side of the membrane and a second catalyst layer arranged onthe second side of the membrane, a frame arranged at least on the firstside of the membrane, wherein the frame encircles the first catalystlayer in a plane of the main extension direction of the first catalystlayer, and a gap between the first catalyst layer and the frame. Anotheraspect of the present invention relates to a membrane assembly for afuel cell which is manufactured by the above-mentioned method. A furtheraspect of the invention relates to a fuel cell with said membraneassembly.

Membrane assemblies, also often referred to as membrane electrodeassembly (MEA), are well-known for usage in a fuel cell. If such amembrane assembly comprises a frame, it is also referred to a membraneelectrode frame assembly (MEFA). A fuel cell is configured to convert afuel, for example, hydrogen, into electrical energy, in particular anelectrical voltage resulting in an electrical current, when a powercircuit is closed.

The membrane assembly for the fuel cell comprises the membrane, alsoreferred to as electrolyte, and the first and second catalyst layer,which also can be referred to as electrodes. A multitude of fuel cellscan be combined to a stack of fuel cells. Each of the fuel cells of thestack can comprise a respective membrane assembly.

Current membrane assemblies, membrane electrode frame assemblies inparticular, are proned to failures at an edge between the frame and thecatalyst layers. Such failures can be caused by chemical degradation inthe region where the catalyst layer and the frame face each other. Inthis region, where the frame and the catalyst layer face, can be a gasdiffusion layer, which goes over the frame. Such a gas diffusion layermay be arranged on both surfaces of the membrane assembly. The chemicaldegradation can be caused by a so-called “local OCV (Open CircuitVoltage)” type condition in this region. The OCV-type degradation occurswhen hydrogen peroxide and associated radicals are formed either byhydron diffusion through the membrane and reacting with oxygen at thecathode or oxygen diffusing through the membrane and reacting withhydrogen at the anode.

Document EP 1 876 666 B1 reveals a polymer electrolyte fuel cellcomprising a stack of one or more cells each having a MEA and anode andcathode separators that sandwich that MEA therebetween. Electrode layersof said fuel cell have a peripheral region.

The present invention is directed to overcoming the above-mentionedproblem of the chemical degradation.

This object is solved by the membrane assembly, the method formanufacturing the membrane assembly and the fuel cell of the independentclaims. Advantageous embodiments and practical improvements aresubject-matter of the dependent claims.

The invention is based on the idea that the degradation, which ismentioned above, is turned off when there are no catalyst layers arepresent in the region of the frame. In other words, it is part of theidea to form the membrane assembly in a way that the first catalystlayer and the frame are fully divided by the gap between them. In otherwords, the gap is supposed to separate the frame from the first catalystlayer. The gap may have a at least substantially constant width. Again,in other words, the width may be the distance by which the frame and thecatalyst layer, especially the first catalyst layer, and the frame areseparated from each other.

The present method is suitable for manufacturing a membrane assembly fora fuel cell, which membrane assembly comprises a membrane with a firstside and a second side, a first catalyst layer arranged on the firstside of the membrane and a second catalyst layer arranged on the secondside of the membrane, a frame arranged at least on the first side of themembrane, wherein the frame encircles the first catalyst layer in aplane of the main extension direction of the first catalyst layer and agap between the first catalyst layer and the frame.

To allow an easy and cost-effective way for manufacturing such amembrane assembly, it is envisaged that the manufacturing methodcomprises the following steps:

-   -   Positioning a first decal layer, which is made of the same        material as the first catalyst layer, on the first side of the        membrane relative to the frame, which is positioned on the first        side of the membrane, in a way that the first decal layer        overlaps the frame,    -   positioning a second decal layer, which is made of the same        material as the second catalyst layer, on the second side of the        membrane, and    -   pressing the first decal layer and the second decal layer        against each other with the membrane and the frame positioned        in-between.

The frame may form a closed loop around the first catalyst layer whenboth are arranged on the first side of the membrane. In some embodimentsit may be envisaged that the frame is arranged on both the first sideand the second side of the membrane. In these embodiments, the frame maycomprise two parts, which are arranged on a different side of themembrane each. In this case, the first side of the membrane may beencircled by a first part of the frame and the second catalyst layer maybe encircled by a second part of the frame. Within the scope of thepresent invention “encircled” means in particular fully encircled. Inother words, the first side of the membrane can be fully surrounded orenclosed by the frame in the plane of the main extension direction ofthe first catalyst layer. Between the first catalyst layer and the frameis a spare region, which forms the gap. In other words, in the gapneither a part of the frame nor a part of the first catalyst layer isarranged on the membrane. As mentioned above, the gap may have aconstant valve between the first catalyst layer and the frame.

The first catalyst layer is made from the first decal layer in a decaltransfer process. The second catalyst layer is made from the seconddecal layer in a decal transfer process. This decal layer process maycomprise the above-mentioned steps of positioning the first decal layerand the second decal layer as well as pressing the first and the seconddecal layer against each other. The inventive manufacturing methodutilizes the fact that the thickness of the membrane and the framepositioned in-between the first and the second decal layer whilepressing them against each other is not constant. The combination ofmembrane and frame has a greater thickness of regions of the membranewhere parts of the frame are arranged on the membrane. In other words,the membrane and the frame have a greater thickness in regions where theframe extends. Analogously, in regions where the frame does not extendthe thickness equals the thickness of the membrane. In regions, wherethe frame extends the thickness equals the thickness of the membraneplus the thickness of the frame. Therefore, in regions where the frameis arranged on the membrane, automatically a higher pressure is appliedcompared to regions of the membrane not covered by the frame. This iseven then ensured, when a press with two respective press surfaces topress the first and the second decal layer against each other is plain.With increasing distance from the frame, the pressure applied whilepressing increases. In other words, the lowest pressure is applied wherethe gap is supposed to be located. As a result of this, the first decallayer does not adhere to the first side of the membrane next to theframe. On a first side of the gap, where the frame is located, the firstdecal layer does equally not adhere, when the frame is made of anappropriate material. In other words, the frame can be made from amaterial where the first decal layer does not adhere to. On a secondside of the gap, where the first catalyst layer is supposed to beformed, the pressure is sufficient to make the first decal layer adhereto the membrane. Therefore, the adhering part of the decal layer formsthe first catalyst layer.

Before the pressing of the first decal layer and the second decal layeragainst each other, both decal layers are positioned. It can beenvisaged that the first decal layer overlaps the frame. Advantageously,the first decal layer has greater dimensions than the region of themembrane which is covered by the frame, the gap and the first catalystlayer together. Said region can be fully overlapped by the first decallayer. The second decal layer may have the same size, at leastsubstantially, like the first decal layer. The second decal layer may bepositioned analogously to the first decal layer but on the second sideof the membrane. For example, the second decal layer may be positionedin a way that its projection into the plane of the membrane equals theprojection of the first decal layer into the plane.

In the next step, both decal layers are pressed against each other. Thishappens while the membrane with the frame positioned on the first sideof the membrane is positioned in-between the first and the second decallayer. While positioning the first and the second decal layer and/orwhile pressing them against each other, the decal layers may be arrangedon a respective substrate. The substrate can fa facilitate the handingof the decal layers and stabilize them while pressing and/orpositioning. The pressing can be done by a hot press. For example, thepressing is carried out by pressing two pressing surfaces with the firstand the second decal layer as well as the membrane and the framein-between against each other. Due to the pressing, both decal layersadhere partly to the first or second side of the membrane. The part ofthe decal layer which adheres to the first side of the membrane can formthe first catalyst layer. The part of the second decal layer whichadheres to the second side of the membrane can form at least essentiallythe second catalyst layer.

Sometimes, another part of the second decal layer may adhere to themembrane on its second side opposite to the regions where the membranetouches the frame on the first side. This can be referred to asadditional catalyst layer. The additional catalyst layer does not affectthe usage properties of the membrane assembly or a fuel cell constructedwith the membrane assembly. An additional gap may be formed on thesecond side of the membrane just in the opposite position of the gap onthe first side of the membrane. This is due to the fact that the firstand the second catalyst layer may have the same extension over therespective side of the membrane.

The present manufacturing method provides an easy way to produce amembrane assembly with a frame and a catalyst layer and with a gapbetween the frame and the catalyst layer. The first and the second decallayer can have a much greater extension than the resulting membraneassembly. It is no careful alignment of the first catalyst layer and theframe relative to each other necessary for providing the gap. Also nocareful alignment of the first catalyst layer and the second catalystlayer relative to each other is necessary. In opposite, the gap isformed automatically during the manufacturing method without precise oraccurate positioning of the frame and the first catalyst layer relativeto each other.

According to a further development of the invention, it is envisagedthat the positioning of the second decal layer is carried out in a waythat the decal layer overlaps the projection of the frame into a planeof the second decal layer. In other words, the second decal layer canoverlap the frame or its projection into the plane of the second decallayer. Advantageously, the overlapping is the same like the overlappingof the first decal layer with respect to the frame. In particular, thesecond decal layer may overlap the frame or its projection respectivelyin every direction. In particular, the second decal layer may overlapthe projection of the frame, the gap and the first catalyst layer intothe plane of the second decal layer. By that it is ensured that thefirst and second catalyst layer are arranged on the membrane on adifferent side each but direct opposite to each other. In other words,the projection of the first and second catalyst layer into the plane ofthe membrane can be at least substantially equal.

According to a further development, the pressing is carried out with twopressing surfaces both overlapping the frame. In other words, the twopressing surfaces can overlap the frame, the gap and the first or thesecond catalyst layer, respectively. By that it is ensured that anappropriate pressure is applied to form the gap, the first and thesecond catalyst layer.

According to a further development, it is envisaged that prior to thepositioning of the first catalyst layer and the second decal layer theframe is arranged on the membrane by a separate pressing procedure. Theseparate pressing procedure can be carried out with the same pressand/or the same two pressing surfaces like the pressing of the first andthe second decal layer against each other. In particular, the separatepressing procedure can be a hot pressing with a hot press. The advantageof the separate pressing procedure is that the frame is already fixed tothe membrane when the positioning of the first and the second decallayer is carried out.

According to another development, it is envisaged that prior to thepositioning of the first decal layer and the second decal layer theframe is positioned on the membrane to be fixed to the membrane in thefollowing of pressing the first decal layer and the second decal layeragainst each other. In other words, only one pressing procedure isenvisaged for both fixing the frame to the membrane and forming thefirst and the second catalyst layer from the respective decal layers.This can result in a more cost-effective production of the membraneassembly.

According to a further development, it is envisaged that a thickness ofthe frame is varied for adjusting the width of the gap. For example,frames of different thickness can be used as they result in a differentwidth of the gap. Other factors, which can be used for adjusting thewidth of the gap are a compliance of the press or calendar materials.All these parameters can be tuned to ensure the gap is catalyst-free inan easy way.

Another aspect of the invention relates to the membrane assembly for afuel cell, comprising:

-   -   A membrane with a first side and a second side,    -   a first catalyst layer arranged on the first side of the        membrane and a second catalyst layer arranged on the second side        of the membrane,    -   a frame arranged on least to the first side of the membrane,        wherein the frame encircles the first catalyst layer in the        plane of the main extension direction of the catalyst layer, and    -   a gap between the first catalyst layer and the frame.

To allow an easy and cost-effective way for manufacturing such amembrane assembly, the membrane assembly is characterized in that

-   -   the first catalyst layer is formed from a first decal layer made        of the same material as the first catalyst layer by decal        transfer and the second catalyst layer is formed from a second        decal layer made of the same material as the second catalyst        layer by decal transfer, and    -   the gap between the first catalyst layer and the frame is formed        by the decal transfer by pressing the first decal layer        overlapping the frame and the second decal layer against each        other with the membrane and the frame in-between.

The membrane assembly is distinguishable from any other membraneassembly due to the different properties of the first and the secondcatalyst layer as a result of the formation from the respective decallayer. The forming of the gap by means of the pressing also results indiffering properties of the gap compared to other membrane assemblies.Especially, the edges of the first catalyst layer facing the gap can bedifferent as well as the width of the gap which is unusual constant.

The resulting membrane assembly has already been discussed within thescope of the manufacturing method. The first catalyst layer and thesecond catalyst layer can be made of the same material. In this case,the first and the second decal layer can also be made from the samematerial. The first and the second catalyst layer can be configured toenhance the transformation of the fuel into the electrical energy. Thefirst and/or the second catalyst layer can be made of an electricallyconductive material. Therefore, they can be referred to as electrodes aswell. The electrodes or the catalyst layers can be configured to conductthe electrical energy or the electrical current to poles of the membraneassembly or a fuel cell respectively, when the membrane assembly is partof the fuel cell.

According to a further development, it is envisaged that the firstcatalyst layer and the second catalyst are (at least substantially)fully overlapping with respect to their extension parallel to themembrane. In other words, the first and the second decal layer may havethe (at least substantially) same projection into the plane of themembrane. For example the first and the second decal layer may have the(at least substantially) same size, extension and position parallel tothe membrane. A precise equivalent positioning of both catalyst layerson both sides of the membrane is ensured by that and may crucial for aadvantageous functioning of the membrane assembly or a fuel cell ofwhich the membrane assembly is part of.

A third aspect of the invention relates to a fuel cell with theabove-mentioned membrane assembly. In other words, the fuel cell maycomprise the above-mentioned membrane assembly. Again in other words,the fuel cell may comprise a membrane assembly which is manufacturedwith the above-mentioned manufacturing method.

The fuel cell can comprise one or more such membrane assemblies. Thefuel cell can be stacked with other fuel cells to a fuel cell stack. Thefuel cells of the fuel cell stack may be connected with withoutmechanically as well as electrically. The fuel from conversion into theelectrical energy may flow through all fuel cells of the fuel cellstack. Also exhaust gases resulting of said conversion can be exhaustedby the same exhaust. The fuel cells of the fuel cell stack can beelectrically connected in parallel or in series or in a combination ofboth.

The fuel cell may further comprise a housing which at least partlysurrounds the membrane assembly. The fuel cell may comprise one or moregas diffusion layers for allowing the fusion of the fuel. A first gasdiffusion layer can, for example, be arranged on the first catalystlayer. The first gas diffusion layer can also extend over the gap and/orthe frame. In other words, the first gas diffusion layer may cover thefirst catalyst layer, the gap and the frame. A second gas diffusionlayer can be arranged on the second catalyst layer. The second gasdiffusion layer may extend over the whole second side of the membrane.Therefore, it may extend over the additional gap on the second side ofthe membrane and/or the additional catalyst layer.

Further advantages, features, and details of the invention derive fromthe following description of preferred embodiments as well as from thedrawings. The features and feature combinations previously mentioned inthe description as well as the features and feature combinationsmentioned in the following description of the figures and/or shown inthe figures alone can be employed not only in the respectively indicatedcombination but also in any other combination or taken alone withoutleaving the scope of the invention.

The drawings show in:

FIG. 1 a schematic cross-section of an excerpt of a membrane assemblywith additional gas diffusion layers;

FIG. 2 exemplary steps for manufacturing the membrane assembly with onepressing procedure;

FIG. 3 a method for manufacturing the membrane assembly with twoseparate pressing procedures;

FIG. 4 a technical apparatus for performing the manufacturing methodwith two pressing steps; and

FIG. 5 a schematic representation of a prototype of the membraneassembly in a cross section.

In the figures the same elements or elements having the same functionare indicated by the same reference signs.

FIG. 1 shows a membrane assembly 1 comprising a membrane 2, a frame 6arranged on the membrane 2 and catalyst layers 3, 4 on both sides of themembrane too. On both sides the membrane assembly 1 is coated is with agas diffusion layer 8, 9. The respective gas diffusion layers 8, 9 canbe either considered a part of the membrane assembly 1 or not part ofthe membrane assembly 1.

The membrane 2, which can also referred to as electrolyte, has a firstside 18 and a second side 19. The membrane 2 can permeable orsemi-permeable to enable an exchange of ions and/or molecules betweenthe first side 18 and the second side 19. A first catalyst layer 3 isarranged on the first side 18 of the membrane 2. A second catalyst layer4 is arranged on the second side 19 of the membrane 2. The frame 6 isarranged on the first side 18 of the membrane 2. The first catalystlayer 3 and the second catalyst layer 4 can be formed as electrodes. Inother words, the catalyst layers 3, 4 can be configured to conduct anelectrical current. The catalyst layers 3, 4 can be made of different orthe same material. Both catalyst layers 3, 4 can be configured tocatalyze a conversion from a fuel into electrical energy. For example,fuel and ambient air or oxygen can be converted to energy and exhaustgases by the catalyst layers 3, 4. When arranged in a fuel cell, themembrane assembly 1 can be arranged to carry out the conversion. Thefuel cell can comprise one or more membrane assemblies 1 and a housing(not shown in the figures).

Catalytic reactions in and around the first catalyst layer 3 can lead todegradation processes at the frame 6. This may happen especially whenthe first catalyst layer 3 and the frame 6 face each other directly. Inother words, the degradation especially occurs where the first catalystlayer 3 and the frame 6 touch each other or are at least very close toeach other. The degradation can be a chemical degradation which iscaused by a local open circuit voltage type condition in this area. Theopen circuit voltage type degradation occurs when hydrogen peroxide andassociated radicals are formed by either hydrogen diffusing the membrane2 and reacting with oxygen at the cathode or oxygen diffusing throughthe membrane 2 and reacting with hydrogen at the anode. This degradationpathway is turned off when there is no catalyst layer 3, 4 present inthis area. Hence, there is a gap 5 between the frame 6 and the firstcatalyst layer 3. In other embodiments not shown in the figures, theframe 6 may be arranged on both sides 18, 19 of the membrane 2. Forexample, the frame 6 may consist of at least two parts, where a firstpart is arranged on the first side 18 and a second part is arranged onthe second side 19. It is also possible that the frame 6 unfolds a matchof the membrane 2 and therefore touches both sides 18, 19 of themembrane 2. If this is the case, the above-mentioned is also valid forthe second catalyst layer 4 and the frame 6. Anyway, there is anadditional gap 12 between the second catalyst layer 4 and a projectionof the frame 6 into a plane of the second catalyst layer 4. In thepresent case, there is an additional catalyst layer 11 in the area ofthe projection of the frame 6 into the plane of the second catalystlayer 4.

A first gas diffusion layer 8 covers the first catalyst layer 3, the gap5 and the frame 6. The region of a thought triangle above the gap 5 isalso referred to as triangle region 7. In other words, all arrangementson the first side 18 are fully covered with the gas diffusion layer 8.In case there would be no gap 5, the triangle region would be locatedbetween the first catalyst layer 3, the first gas diffusion layer 8 andthe frame 6. A second gas diffusion layer 9 is arranged on the secondcatalyst layer 4 and the additional catalyst layer 11. The secondcatalyst layer 9 also covers the additional gap 12. Analogously, the gap5 is covered by the first gas diffusion layer 8.

Now referring to FIG. 2, a first possibility for manufacturing themembrane assembly 1 is shown. In a first step S1.1 of the exemplarymethod, the membrane 2, the frame 6, a first decal layer 13 and a seconddecal layer 14 are positioned relative to each other. More precisely,the second decal layer 14 is positioned on the second side 19 of themembrane 2. The frame 6 is positioned on the first side 18 of themembrane 2. The first decal layer 13 is also positioned on the firstside 18 of the membrane 2. The position of the first decal layer 13 iscarried out in a way that it overlaps the frame 6. In other words, theframe 6 is positioned between the membrane 2 and the first decal layer13. Hence, the frame 6 touches the first side 18 of the membrane 2 withits first side and the frame 6 touches the first decal layer 13 with itssecond side. The first side and the second side of the frame 6 can be atleast substantially parallel to each other. Both decal layers 13, 14 arearranged on a respective backer 10. The backer 10 or substrate makes ahandling of the respective decals 13, 14 easier. In other words, thebacker 10 facilitates the handling of the decal layers 13, 14. In afollowing step S1.2, the whole arrangement of decal layers 13, 14,membrane 2 and frame 6 is pressed in a pressing procedure 20. By thepressing procedure 20 the frame 6 gets firmly connected to the membrane2. Also parts of the decal layers 13, 14 are getting firmly connected tothe membrane 2. In particular, the first decal layer 13 gets partlyattached to the first side 18 of the membrane 2. The part of the firstdecal layer 13 which gets attached to the membrane 2 forms the firstcatalyst layer 3. In particular, the second decal layer 14 gets partlyattached to the second side 19 of the membrane 2. The part of the seconddecal layer 14 which gets attached to the membrane 2 forms the secondcatalyst layer 4. This can be seen in step 1.3. Therefore, the firstdecal layer 13 is made of the same material as the first catalyst layer3. Analogously, the second decal layer 14 is made of the same materialas the second catalyst layer 4. If both catalyst layers 3, 4 consist ofthe same material, both decal layers 13, 14 may be equal.

In the step S1.2 due to the presence of the frame 6 in the triangleregion 7, less pressure is applied compared to the region where therespective catalyst layers 3, 4 are formed. Of course, a relatively highpressure is also applied where the frame 6 is. Because there the firstdecal layer 13 does not connect properly to the frame 6, the decal layerremains on the backer 10, where the frame 6 and the first decal layer 13face without. On the second side 19 of the membrane 2 the decal layeralso gets attached to the membrane 2 opposite the frame 6. This leads tothe formation of the additional catalyst layer 11. This additionalcatalyst layer 11 is not necessary for the function but does not anyharm to the fuel cell or the membrane assembly 1. Due to the lowerpressure during the pressing procedure 20, neither the first decal layer13 nor the second decal layer 14 are getting attached to the membrane 2in the area of the gap 5 and the additional gap 12. This is the desiredeffect of the present manufacturing method.

In another possible manufacturing method two pressing procedures 21, 24are envisaged in opposite to the single pressing procedure 20. A step bystep diagram is shown in FIG. 3. In a first step S2.1, the frame 6 getspositioned on the membrane 2 and pressed in a first separate pressingprocedure 21. During the first separate pressing procedure 21, the frame6 gets attached to the first side 18 of the membrane 2. During the firstpressing procedure 21, the membrane 2 can be attached to a backer 30 orsubstrate. Analogously to the backer 10 of the decal layers 13, 14, thebacker 30 can facilitate the handling of the membrane 2. After the firstpressing procedure 21, the backer 30 gets removed from the membrane 2.This can happen in a step S2.2. In a following step S2.3, both decallayers 13, 14 are positioned on the membrane 2. This step can beunderstood analogously to step S1.1, as the decal layers 13, 14 have tobe positioned relative to the membrane 2 and the frame 6 the same way.In particular, the first decal layer 13 is positioned on the first side18 of the membrane 2 in a way that the first decal layer 13 overlaps theframe 6. In particular, the second decal layer 14 is positioned on thesecond side 19 of the membrane 2. Advantageously, the second decal layer14 is positioned in a way that the decal layer 14 overlaps theprojection of the frame 6 into a plane of the second decal layer 14.

In a step S2.4, a second pressing procedure 24 is carried out. By thatpressing procedure 24, the first catalyst layer 3 and the secondcatalyst layer 4 are formed. In a step S2.5, the pressure is removed andthe backers 10 are removed. The result is literally the same asdescribed above according to the steps S1.2 and S1.3. Pressing surfaces22 and 23 used for the respective pressing procedures 21 and 24 can bethe same or different. The pressing surfaces 22 and/or 23 may be part ofa hot press or a respective hot press. Hence, the pressing procedures 21and 24 can be hot pressing procedures. Analogously, the pressingprocedure 20 can be a hot pressing procedure.

FIG. 4 shows an example for an apparatus to perform the manufacturingmethod according to FIG. 3. The pressing surfaces 22 can be provided byrollers 25, each. Analogously, the pressing surfaces 23 can be providedby respective rollers 26. The apparatus should briefly be described inthe following:

The membrane 2 and its backer 30 and together with the frame 6 get intothe rollers 25. The rollers 25 are performing the first pressingprocedure 21. Due to the continuous process in which the membrane 2moves to the right according to FIG. 1, the rollers 25 provide asingular effect like the plane pressing surfaces 22. After the firstpressing procedures 21 in-between the two rollers 25, the backer 30 isremoved from the membrane 2. The result is a framed membrane 16 as anintermediate product. For the second pressing procedure 24 realized bythe rollers 26, both decal layers 13, 14 are provided on theirrespective backer on the respective side of the membrane or the framedmembrane 16, respectively. So just before the rollers 26, the step S2.3is carried out. In-between the rollers 26, the step S2.4 or the secondpressing procedure 24 is carried out. When leaving the rollers 26, bothbackers 10 are removed. That equals the step S2.5. The result is theendless role of membrane assemblies 17.

Finally, FIG. 5 shows a cross section of an excerpt of the membraneassembly 1. FIG. 5 is a drawing of a prototype manufactured with thepresent manufacturing method according to FIG. 2 or FIG. 3. In FIG. 5can be seen that both catalyst layers 3 and 4 are aligned to each othervery well. The difference of size and/or alignment d1 was approximately10 μm. In other words, bot catalyst layers 3, 4 are positioned oppositeto each other within the neglectable tolerance of 10 μm. A width d2 ofthe gap 5 equals 500 μm in the prototypes. It should be mentioned thatthe give measures for d1 and the width d2 are only exemplary.Nevertheless, both measures have proven to be useful in practicalexamples.

REFERENCE SIGNS

1 membrane assembly

2 membrane

3 first catalyst layer

4 second catalyst layer

5 gap

6 frame

7 triangle region

8 first diffusion layer

9 second diffusion layer

10 backer

11 additional catalyst layer

12 additional gap

13 first decal layer

14 second decal layer

16 framed membrane

17 membrane assemblies

18 first side

19 second side

20 pressing procedure

21 pressing procedure

22 pressing surfaces

23 pressing surfaces

24 pressing procedure

25 rollers

26 rollers

30 backer

S1.1 . . . S1.3 steps

S2.1 . . . S2.5 steps

The invention claimed is:
 1. A method for manufacturing a membraneassembly for a fuel cell, which membrane assembly comprises a membranewith a first side and a second side, a first catalyst layer arranged onthe first side of the membrane and a second catalyst layer arranged onthe second side of the membrane, a frame arranged at least on the firstside of the membrane, wherein the frame encircles the first catalystlayer in a plane of the main extension direction of the first catalystlayer, and a gap between the first catalyst layer and the frame, themethod comprising the following steps: positioning a first decal layer,which is made of the same material as the first catalyst layer, on thefirst side of the membrane relative to the frame, which is positioned onthe first side of the membrane, in a way that the first decal layeroverlaps the frame, positioning a second decal layer, which is made ofthe same material as the second catalyst layer, on the second side ofthe membrane, pressing the first decal layer and the second decal layertowards each other with the membrane and the frame positionedin-between, wherein with increasing distance from the frame, thepressure applied while pressing increases, resulting in the first decallayer not adhering to the first side of the membrane next to the frame.2. The method according to claim 1, wherein the positioning of thesecond decal layer is carried out in a way that the second decal layeroverlaps a projection of the frame into a plane of the second decallayer.
 3. The method according to claim 1, wherein the pressing iscarried out with two pressing surfaces both overlapping the frame. 4.The method according claim 1, wherein prior to the positioning of thefirst decal layer and the second decal layer the frame is arranged onthe membrane by a separate pressing procedure.
 5. The method accordingto claim 1, wherein prior to the positioning of the first decal layerand the second decal layer the frame is positioned on the membrane to befixed to the membrane in the following step of pressing the first decallayer and the second decal layer against each other.
 6. The methodaccording to claim 1, wherein a thickness of the frame is varied foradjusting the width of the gap.